Conventionally, a headphone, an earphone (wearable speaker), and the like are known as devices that can be worn on a human body to listen to sound. However, a headphone is used to listen to a sound by pressing and wearing sounding bodies (speakers) so as to cover both ears, whereas an earphone is worn by inserting a sounding body into an ear canal to listen to a sound. Therefore, a sound emitted other than from the headphone during the use of the headphone or earphone is difficult to listen to in some cases, which may lead to danger or inconvenience depending on the use situation. Also, a headphone and an earphone are not designed to accommodate the use for simultaneously listening to a sound from the headphone or earphone and a sound emitted from other than the headphone or the like.
Among devices that are worn on a human body to listen to a sound, a bone conduction speaker is known as a device that avoids blocking the ear. Patent Document 1 (identified below) discloses a bone conduction speaker that directly transmits voice information to an inner ear through air by pressing a vibrator against a skin on bone tissue such as near an auricle and mandibular bone through the bone tissue without passing through a middle ear transmission system. With this bone conduction speaker, it is possible to simultaneously listen to a sound from the speaker and a sound emitted other than from the speaker without blocking the ear.
Patent Document 1: Japanese Patent Application Laid-Open No. 2007-104548.
However, the bone conduction speaker disclosed in Patent Document 1 transmit a sound by vibrating a vibrator when a sound signal is input and pressing and wearing the vibrator on the skin on the bone tissue. Therefore, the bone conduction speaker is configured to vibrate the vibrator when a sound signal is input, regardless of whether the vibrator is pressed and worn on the skin on the bone tissue. Even while not listening to a sound, electric power is consumed. Likewise, a conventional headphone and earphone consume electric power even while not listening to a sound because a sounding body generates a sound when a sound signal is input, regardless of whether the headphone or earphone is worn on the ear.